I was walking behind Notre Dame in Paris - typical tourist place - when a Rom girl came up to me with a petition to sign. She was a bit insistent so I grabbed her right wrist - and recovered my mobile phone from her left hand - I had rather foolishly left it in a belt case.
Here's another illustration of the method from St Petersburg in Russia. The lens is stolen under cover of a paper and passed to an accomplice
LiveLeak.com - Thieves in Saint-Petersburg (Russia) Steal Camera lens from a photographer
I was thinking of going to full-frame for holidays but finally I can see that the compactness of the DX format is less visible to thieves..